Electrochemical lithium accumulators operate based on the principle of lithium insertion or deinsertion (or intercalation-deintercalation) on at least one electrode.
They comprise an electrochemical anode/electrolyte/cathode core which may be integrated in a structure having a cylindrical, prismatic, or stacked geometry, for example. The two electrodes each comprise a current collector and are separated by a separator which can appear in solid or polymeric form (membrane).
Generally, the accumulator core is protected from external elements by a rigid or flexible package.
The accumulator may thus be contained in a metal package (FIG. 1), for example, made of aluminum. This type of package is generally designed to comply with different types of constraints: electrical (relative to the flowing of the electric current); mechanical; thermal; or safety (safety vents on the package). Generally, the package is sealed by welding, for example, by means of a laser, which gives it tightness properties along time. Further, the accumulator operation is ensured by the presence of connections external to the package.
Although the use of a metal package provides many advantages, its weight non-negligibly affects the energy density of the accumulator.
To overcome this problem, flexible packages have been developed. It generally is a multilayer film containing one or a plurality of polymer films laminated by gluing to a thin central aluminum foil (FIGS. 2 and 3). The electric connections are ensured by means of current collection tabs which cross the flexible package. This type of package enables to increase the energy density relative to a same cell in a rigid package. Further, the internal layer of a flexible package, that is, the layer in contact with the electrochemical core, is insulating. It generally is a heat-sealable polymer (polyolefin), which is inert with respect to the electrochemical core, thus enabling to isolate the Li-ion cell from the ambient atmosphere and from the central aluminum foil.
A flexible package thus enables to comply with the requirements of energy density of the accumulator and of flexibility. It has however been observed that the chemical resistance of the sealing of a cell in a flexible package of prior art deteriorates along time.
Further, although the two types of available packages, flexible or rigid, each have advantages, the energy density of accumulators still has to be improved. Indeed, each of the essential components of accumulators generally has a single function, which generates an overweight. For example, in the case of a conventional cell in a flexible or rigid package, the current collectors ensure the conduction of electrons from the electrodes to the outside of the cell, while a second package is added to reinforce the resistance to shocks and to vibrations of the cell.
Thus, to improve the energy density of accumulators, Li-ion cell current collectors in the form of metal foams (aluminum, nickel . . . ) have been described in prior art. Such materials enable to increase the active surface area of the current collector while lightening the cell weight.
For shock resistance, the introduction of a polymer foam between the unit cells of an accumulator has been described in prior art. The foam can thus absorb the shock of a plurality of cells.
Although such solutions may seem satisfactory when considered individually from one another, the general weight of accumulators still needs to be limited.
The Applicant has developed a trifunctional component ensuring at the same time:                the packaging of the Li-ion cell, that is, its isolation from the outer atmosphere;        the role of an elastic current collector;        the safety of the Li-ion cell in terms of resistance to shocks and to vibrations.        